Tool holder assemblies configured for use with interchangeable cutting or machining tools provide a number of process efficiencies. A smaller number of machine spindles, for example, can be employed for a larger variety of machining operations, and downtime between various cutting tasks can be reduced by decreased need to switch apparatus for each machining application. In order to realize the foregoing efficiencies, tool coupling systems must provide secure connection with minimal tool change downtime while maintaining desired operating tolerances.
In many applications, hydraulic chucks are employed in rotary tool holder assemblies. A hydraulic chuck generally comprises an expansion sleeve defining a clamping bore. A single, circumferential expansion chamber resides between the sleeve and chuck body. Tightening a piston clamping screw exerts force on a pressure piston, which in turn pressurizes hydraulic fluid or silicone fluid residing in the chuck body. Such pressure causes the expansion sleeve to compress around the tool shank, creating a highly concentric clamping force with high torque transmission capability. However, hydraulic chucks can suffer from low radial stiffness when a side force is applied to a tool at a certain distance from the sleeve, resulting from hydraulic fluid displacement from side to side in the circumferential chamber.